1. Field of the Invention
This invention relates to a data recording and playback apparatus using a helical scan system for recording and playing back data on magnetic tape, and more particularly to tracking technologies thereof.
2. Description of the Related Art
A conventional data recording and playback apparatus for recording and playing back general digital data on magnetic tape adopts a recording system with fixed heads. However, in recent years, the necessity for increasing the storage capacity of magnetic tape has been raised and it is expected to provide a data recording and playback apparatus adopting a helical scan system which can record a larger amount of data on magnetic tape than the fixed head recording and playback system.
The helical scan system is a recording system widely adopted for video tape recorders (VTRs). With general VTRs, control tracks scanned by a linear scan system are provided on magnetic tape besides video tracks scanned by the helical scan system. When data is recorded on the video tracks, a signal indicating a reference timing is recorded on the control track. At a time of playback, the signal on the control track is played back in parallel with the playing-back of the signals on the video tracks and a reel and capstan are controlled based on the reference signal playback timing and a head cylinder rotation phase, thereby tracking the video tracks. In VTRs such as the type C standardized by the SMPTE (Society of Motion Picture and Television Engineers), tracking is performed using a dither method by which a track shift and shift direction are determined in response to the amount of the drop in a level of a playback signal when a head is moved only a little.
The D2 format digital video tape recorder (DVTR) standardized by the SMPTE is known as an apparatus using the helical scan system for recording digital video data on magnetic tape. Such a DVTR is described in ITEJ Technical Report, Vol.11, No. 24, pp. 13-18, VR' 87-30 (October 1987), etc.
When general digital data is recorded and played back, the reliability of data being recorded and played back is required to be higher than that of data for VTRs. Therefore, recording and playback in a recording format which can secure more accurate tracking and higher reliability than those of VTRs are required to provide a data recording and playback apparatus using the helical scan system for recording digital data. On the other hand, to store a larger amount of data on magnetic tape, it is desired to eliminate linear tracks for tracking, such as the control tracks, in order to be able to use the linear track area as a recording area for digital data.